You can get m/f towels really cheap from asda their usually six A4 sized towels for 3quid or one big towel for the same price, they also sell good mitts. I got my wheel brushes from there at two pound each.
Plus the towels are all different colours so it makes it easy to designate them to certain tasks (drying, buffing etc)

Bought a snow foam lance for my pressure washer & a Gilmour Foamaster to use on the hosepipe, have tried various snow foams and am currently using Chemical Guys No Touch

Bought Chemical Guys buckets and grit guards so I can wash using the two bucket method

I use Dooka wash mits as they seem to hold half a gallon of water

Lots of drying towels, micro fibre cloths, german applicator pads and various other foam and micro fibre applicators

I even bought a rotary polisher and pads a couple of years ago and machine polished my old Octavia estate

Numerous different brushes of all shapes and sizes and lots of different interior cleaners/dressings - the best all round, multi-purpose cleaner I have come across is Meguiars all purpose cleaner

Gtechniq products have cost me the most I think!

I think the decontamination stage is the most important - I usually use Iron X to remove the fallout and Tardis to remove the tar spots - have clayed cars in the past but have now moved to a decon block

Once you get into car detailing it will drain your wallet. I'm a big fan of Meguiars products but have loads of stuff I've tried and wasn't impressed with. If you really want to improve the paintwork try claying the car in between washing and polishing. You can find videos on YouTube showing you how to do it. My normal procedure is snow foam, clean off with pressure washer, wash with Meguirars shampoo & microfibre mitt, rinse, dry off with huge micro fibre towel, clay, rinse, dry, polish using a dual action polisher, wax, clean trim and finally clean the glass.

I pretty much follow Emma's step by step approach, which isn't surprising because I'm lurking over at DW a lot too.

If you're in a rush and you've got a proper snow foam lance, the Demon Snow Foam Shampoo can do the pre-wash and wash in one go. Spray on the foam, wait a few minutes, then use a wash mitt to wash the car properly with the remaining snow foam. The Demon Foam can be used as shampoo in a bucket anyway so works out alright.